1. Field of the Invention
The present invention relates generally to an apparatus and method for saving power in a dual mode portable terminal, and in particular, to an apparatus and method for saving power of an unlicensed band network supporting module in a dual mode portable terminal that concurrently supports a cellular network and the unlicensed band network. The unlicensed band network refers to a network using an unlicensed Industrial, Science, and Medical (ISM) radio frequency band. For example, there are Wireless Fidelity (WiFi), IEEE 802.11, HIgh PErformance Radio Local Area Network (HIPERLAN), Bluetooth® (hereinafter, “Bluetooth”), IEEE 802.15.4, Ulta-WideBand (UWB), etc.
2. Description of the Related Art
Portable terminals supporting a handover between a cellular network and an unlicensed band network and moving and communicating between the cellular network and the unlicensed band network in all voice and data sessions are being currently provided.
Portable terminals supporting both a cellular network and an unlicensed band network periodically search a wireless base station (or an Access Point (AP)) of a neighbor unlicensed band network in an idle state and associate with an AP having an optimal condition. Alternately, the portable terminals associate with an AP selected by a user and attempt to access the unlicensed band network. The portable terminals disassociate from the AP automatically when a Received Signal Strength Indicator (RSSI) from the AP falls below a predetermined threshold value.
FIG. 1 is a flowchart illustrating a mode conversion procedure for saving power in a dual mode portable terminal according to the conventional art. For example, a portable terminal supporting a WiFi network that is an unlicensed band network and a cellular network will be described.
Referring to FIG. 1, in Step 101, the portable terminal checks whether the portable terminal associates with a specific AP and accesses the WiFi network. If so, in Step 103, the portable terminal measures a Received Signal Strength Indicator (RSSI) from the AP. In Step 105, the portable terminal compares the measured RSSI with a threshold value for disassociating from the AP. When the measured RSSI is greater than the threshold value for disassociating from the AP, the portable terminal returns to the Step 103 and again periodically measures the RSSI from the AP and performs subsequent steps.
In Step 107, the portable terminal disassociates from the AP when the measured RSSI is less than or equal to the threshold value for disassociating from the AP. In Step 109, the portable terminal performs a state transition to a low power mode. In the low power mode, after turning OFF, a WiFi module (e.g., a WiFi chip) supporting the WiFi network turns ON at every time interval and receives a signal from the WiFi network. After that, a procedure according to the conventional art is terminated.
As described above, the conventional portable terminal performs a state transition to a low power mode and saves power of the portable terminal, when disassociating from an AP because RSSI from an AP that is currently in association falls below a predetermined threshold value. The portable terminal again associates with an AP and converts the low power mode into a general mode, when the RSSI is greater than the predetermined threshold value.
Accordingly, if an RSSI from an AP that is currently associated with the portable terminal temporarily falls below the predetermined threshold value and again increases higher than the predetermined threshold value because of a change of radio wave, the conventional portable terminal repeatedly performs the state transition between the low power mode and the general mode.
However, the portable terminal temporarily consumes a large amount of power when performing a state transition from a low power mode to a general mode or a state transition from a general mode to a low power mode. For example, during a one-time state transition, the portable terminal consumes as much as power as the portable terminal consumes during approximately 500 ms in a general mode. Accordingly, the conventional portable terminal has a drawback that when RSSI from an AP varies because of a change of radio wave, an unnecessary state transition is repeatedly performed and thus power is wasted.